“This is illustrative of the NRCC’s commitment to winning Arizona’s 9th Congressional District and holding Kyrsten Sinema accountable for her extreme record,” Scarpinato said, referring to the Democratic nominee.

Republican Vernon Parker, the former mayor of Paradise Valley, is locked in a tight race with Democratic former Sen. Kyrsten Sinema in a district that is arguably the most competitive in Arizona. Republicans hold a slight voter registration advantage in CD9, while Democrats hold a slight performance edge. Voters in the district supported President Barack Obama in 2008 and supported Democratic candidates for governor and attorney general in 2010.

Scarpinato said he did not know whether the ads would be primarily pro-Parker or anti-Sinema.

Sinema campaign manager Rodd McLeod said they always expected a competitive race, but was confident about Sinema’s chances.

“All the public polling in this race so far shows Sinema that has a lead in this district that President Obama is going to win, and we don’t think that Vernon Parker has the right priorities or the right values to represent Arizona in Congress.”

A recent poll commissioned by Sinema’s supporters showed her leading Parker by four points, within the margin of error. An earlier poll conducted by the Parker campaign a week after the Aug. 28 primary showed him leading by two points, also within the margin of error.

NRCC likely won’t be alone on the air in CD9 for long, and despite its $900,000 ad buy, it may get outspent by the other side. According to Federal Communication Commission records, the Democratic Congressional Campaign Committee has bought about $1 million in airtime in the Phoenix area, and the committee said it has reserved about $2.8 million in the Valley through the week of the general election.